Vehicles are typically incapable of moving in a side-ways or lateral direction. As a result, when parallel parking, a driver must enter the spot at an angle, and then adjust so that the vehicle's length is parallel to the street and the two outer wheels are sufficiently close to the street's edge.
Difficulty arises when two parked cars lie on both sides of a potential parking spot. In this case, the driver must parallel park while avoiding contact with the parked cars. This typically involves backing into the potential spot at a severe angle with respect to the street's edge, then gradually softening the angle as the rear of the vehicle slides into place.
To improve a driver's experience, car manufacturers have recently introduced automatic parking programs (“autopark”). When activated, autopark is capable of automatically parallel parking a car. The vehicle autoparks by measuring the potential parking spot's dimensions with a sensor, then applying a mathematical model to the dimensions to generate the proper speed, approach angle, etc. for parallel parking. Autopark programs can safely parallel park a car faster than an experienced driver.
A problem with existing autopark programs is that they require user-activation via a button or command. As a result, some drivers forget to initiate autopark and manually park their car in a parking spot. As a result, traffic may build up behind the driver, among other potential problems.